1. Field of the Invention
This invention relates to a method of and an apparatus for successively forming slide fastener coupling elements by transversely cutting a blank wire of a generally Y-shape cross section with repeated rolling, and more particularly to a method of and an apparatus for forming coupling elements for slide fasteners suitable for use with quality products.
2. Description of the Related Art
Conventional slide fastener coupling element forming methods of the described type are chiefly divided into two groups: one in which generally Y-shape coupling elements are formed by successively punching a continuous length of flat belt-shape metal plate and, at the same time, bulges for successive coupling heads are formed one at a time (the resulting coupling elements will be hereinafter called "metal-plate coupling elements"); and the other in which individual coupling element blanks are obtained by threading a continuous length of blank wire through a plurality of rollers to shape it into a generally Y shape in cross section and then by successively cutting it into slices of a predetermined thickness using a coacting cutting punch and die, whereupon a bulge is formed at the individual coupling head of the coupling element using by a coacting bulge forming punch and die (the resulting coupling elements will be hereinafter called "wire coupling elements"). The former conventional method is exemplified by Japanese Utility Model Publication No. Sho 62-16886, and the latter conventional method is exemplified by Japanese Patent Publication No. Sho 59-27667. Subsequently, the coupling elements obtained by either conventional method are individually collected loose, or are successively attached to a fastener tape on the same apparatus.
In forming the coupling elements from a metal plate, though it is possible to freely design the coupling elements in a best shape required to be clenched on the fastener tape and in such a shape as not to obstruct the movement of a slider of the slide fastener, the rate of the non-punched-out section to the punched-out section would be fairly large for a desired shape, causing a large amount of loss of material more than the amount of products. Yet if this loss could be reduced to a minimum, it would be difficult to realize the best shape.
Further, since their cut surfaces appear on the surface of the products, the metal-plate coupling elements would make a poor show, depending on the sharpness of the press. Therefore, to obtain a quality product, the metal-plate coupling elements thus obtained are polished and then plated. Besides, since a bulge for the head portion of the coupling element is formed by the press simultaneously with cutting by the press, the bulge is apt to be misshaped to give a great influence on the sliding resistance of a slider.
In forming the coupling elements from a blank wire, since the wire coupling elements formed in a generally Y-shape cross section is successively cut into slices of a predetermined thickness perpendicularly to the blank wire, it is possible to achieve a very high rate of production with no loss of material. However, in order to avoid interference of rollers, since the Y cross-sectional shape and the distance of V leg portions in particular would be influenced resulting from the use of rollers when shaping the blank wire in a generally Y-shape cross section, it is impossible to secure an optimum Y-shape cross section. It is common knowledge that for various reasons described below, the distance between the V leg portions should preferably be minimum as long as the coupling element can be attached to the fastener tape. Nonetheless, since the inner surfaces of the leg portions are pressed by the rollers, the distance between the opposite leg portions cannot be set to less than the diameter of the roller.
Since either of the metal-plate coupling elements and the wire coupling elements are formed by punching, by pressing or by cutting, the resulting coupling elements would not have smooth cut surfaces and hence must be polished on such rough surfaces. In an effort to give a higher quality touch, the coupling elements should preferably be provided with surface treatment such as plating.
Assuming that the coupling elements attached to the fastener tape directly upon termination of forming process are to be provided with finishing treatment such as plating, it would be very difficult to realize such surface treatment to the coupling elements, which are mounted on the insulating fastener tape, in view of the increased cost of production as well as the complicated apparatus structure. Besides it is difficult to even polish the leg portions.
Conventionally, in order to give a higher quality touch, formed coupling elements are individually collected and are then provided with a surface treatment such as polishing or plating before being attached to the fastener tape. After this surface treatment, the coupling elements are conveyed to a fastener element mounting machine where the coupling elements are mounted successively on the inner longitudinal edge of the fastener tape at a predetermined pitch as the opposite leg portions of the individual coupling element are clenched on the inner longitudinal tape edge.
Therefore, for keeping the treated surfaces of the coupling elements free from cracks due to deformation of the leg portions when they are clenched, it should be preferable to set the initial distance of the opposite leg portions as small as possible. The metal-plate coupling elements are free of cracks since the initial distance of the opposite leg portions can be set freely; but, since alot of loss of material is inevitable when the coupling elements are punched out from the metal sheet, the metal-plate coupling elements would require an increased cost of production and would not be practical. On the other hand, the wire coupling elements are easy to manufacture and inexpensive; but, since the contour of the wire coupling elements is shaped by rolling, the initial distance of the opposite leg portions cannot be so small, which would make the coupling elements apt to be cracked.